Another common cause if that is having a bad solder joint or connection point that goes open circuit once it warms up a bit and causes what appears to be a false overheat shutdown.
Just for a heads up typical duty cycle ratings are based on a specific current output over a 10 minute period so your machine should be good for doing roughly 6 minutes of continuous work at or below a certain output rating how ever if you are running above that the duty cycle gets lower and in the case of many low end cheaply built machines run at or near the maximum output could have less than a 10% duty cycle.